Erasable dense paper and improved method of manufacturing

Abstract

A paper which affords complete erasability of typewriter images is disclosed. The paper comprises a web of cellulosic fibers and a blend of a rigid polymeric material and a compatible filler together with a small but effective amount of tin carried by the web. A process for manufacturing the paper is also disclosed.

I claim: 
     
       1. A process for manufacturing dense paper comprising the steps, performed in the following sequence, of: advancing a web of paper having a dry uncalendered density in a range of between about 7 to about 14 lbs./mil.;   applying to the advancing web an aqueous dispersion containing a blend of a rigid polymeric material and an inorganic filler, said blend consisting essentially of from about 35 to about 90% of said polymeric material, from about 10 to about 65% of said inorganic filler, and an organic compound of tin in a range of about 0.10% to about 2.0%, said percentages being by weight based on the non-tin portion of the weight of the blend, said rigid polymeric material having a glass transition temperature in a range of between about 15 to about 60° C.;   removing the excess dispersion from said web; and   heating said web after the excess dispersion has been removed to fuse said blend to said web so that the resulting paper comprises in a range of between about 8.5% to about 50%, by weight of the blend, said weight being based on the dry weight of the web.   
     
     
       2. The process according to claim 1 wherein said organic compound of tin is in a range of about 0.10% to about 2.0%, by weight, based on the combined weight of the polymeric material and filler. 
     
     
       3. The process according to claim 2 wherein said organic compound of tin includes dialkyl tin dicarboxylates. 
     
     
       4. The process according to claim 3 wherein said dialkyl tin dicarboxylates include an alkyl group having at least four carbon atoms. 
     
     
       5. The process according to claim 4 wherein said alkyl group has about eight carbon atoms. 
     
     
       6. The process according to claim 3 wherein said dialkyl tin dicarboxylates include a carboxyl group having a chain of at least twelve carbon atoms. 
     
     
       7. The process according to claim 3 wherein said dialkyl tin dicarboxylates are selected from the group consisting of dioctyl tin dilaurate, dibutyl tin distearate, dibutyl tin di 2-ethyl-hexoate, dibutyl tin di B-mercapto propionate, dibutyl tin dilaurate, dibutyl tin diacetate, and dioctyl tin di b-isooctyl mercapto acetate. 
     
     
       8. The process according to claim 1 wherein said compound of tin is selected from the group consisting of dilauryl tin dichloride and tri n-butyl tin oxide. 
     
     
       9. The process according to claim 1 wherein said blend is impregnated in said web. 
     
     
       10. The process according to claim 1 wherein said blend is carried predominately on the surface of said web. 
     
     
       11. The process according to claim 1 wherein the density of said paper web prior to application of said blend is in a range of between about 8.5 to about 10.5 lbs./mil. 
     
     
       12. The process according to claim 1 wherein said web is substantially free of sizing prior to application of said blend. 
     
     
       13. The process according to claim 1 wherein said polymeric material of said blend is selected from the group of materials consisting of polyvinyl acetate, polyacrylate, and polyvinyl chloride. 
     
     
       14. The process according to claim 1 wherein said inorganic filler is selected from the group of fillers consisting of clay, calcium carbonate, mica, and talc. 
     
     
       15. The process according to claim 1 wherein said aqueous dispersion includes between about 12.5 and 60%, by weight, of said blend, based on the total weight of said dispersion.